.TH GREP 1 
.SH NAME
grep, egrep, fgrep \- search a file for a pattern
.SH SYNOPSIS
.B grep
[ option ] ...
expression [ file ] ...
.LP
.B egrep 
[ option ] ...
[ expression ]
[ file ] ...
.PP
.B fgrep
[ option ] ...
[ strings ]
[ file ]
.SH DESCRIPTION
Commands of the
.I grep
family search the input
.I files
(standard input default)
for lines matching
a pattern.
Normally, each line found
is copied to the standard output;
unless the
.B \-h
flag is used,
the file name is shown if there is more than one input file.
.PP
.I Grep
patterns are limited regular expressions in the style of
.IR ed (1);
it uses a compact nondeterministic algorithm.
.I Egrep
patterns are full regular expressions;
it uses a fast deterministic algorithm that
sometimes needs exponential space.
.I Fgrep
patterns are fixed strings; it is fast and compact.
.PP
The following options are recognized.
.TP
.B \-v
All lines but those matching
are printed.
.TP
.B \-c
Only a count of matching lines is printed.
.TP
.B \-l
The names of files with matching lines are listed (once)
separated by newlines.
.TP
.B \-n
Each line is preceded by
its line number in the file.
.TP
.B \-b
Each line is preceded by the block number
on which it was found.
This is sometimes useful in locating
disk block numbers by context.
.TP
.B \-s
No output is produced, only status.
.TP
.B \-h
Do not print filename headers with output lines.
.TP
.B \-y
Lower case letters in the pattern will also match
upper case letters in the input
.RI ( grep
only).
.TP
.BI \-e " expression"
Same as a simple
.I expression 
argument,
but useful when the
.I expression
begins with a \-.
.TP
.BI \-f " file"
The regular expression
.RI ( egrep )
or string list
.RI ( fgrep ) 
is taken from the
.I file.
.TP
.B \-x
(Exact) only lines matched in their entirety are printed
.RI ( fgrep
only).
.PP
Care should be taken when
using the characters
$ * [ ^ | ? \' " ( ) and \e in the
.I expression
as they are
also meaningful to the Shell.
It is safest to enclose the
entire
.I expression
argument in single quotes \' \'.
.PP
.I Fgrep
searches for lines that contain one of the (newline-separated)
.I strings.
.PP
.I Egrep
accepts extended regular expressions.
In the following description `character' excludes
newline:
.IP
A \e followed by a single character
matches that character.
.IP
The character ^
($) matches the beginning (end) of a line.
.IP
A 
.B .
matches any character.
.IP
A single character not otherwise endowed with special
meaning matches that character.
.IP
A string enclosed in brackets [\|]
matches any single character from the string.
Ranges of ASCII character codes may be abbreviated
as in `a\-z0\-9'.
A ]
may occur only as the first character of the string.
A literal \- must be placed where it can't be
mistaken as a range indicator.
.IP
A regular expression followed by * (+, ?) matches a sequence
of 0 or more (1 or more, 0 or 1)
matches of the regular expression.
.IP
Two regular expressions concatenated
match a match of the first followed by a match of 
the second.
.IP
Two regular expressions separated by | or newline
match either a match for the first or a match for the
second.
.IP
A regular expression enclosed in parentheses
matches a match for the regular expression.
.LP
The order of precedence of operators
at the same parenthesis level
is [\|] then
*+? then concatenation then | and newline.
.SH "SEE ALSO"
ed(1),
sed(1),
sh(1)
.SH DIAGNOSTICS
Exit status is 0 if any matches are found,
1 if none, 2 for syntax errors or inaccessible files.
.SH BUGS
Ideally there should be only one
.I grep,
but we don't know a single algorithm that spans a wide enough
range of space-time tradeoffs.
.PP
Lines
are limited to 256 characters;
longer lines are truncated.
